Veneer lathes are commonly used in the lumber industry to remove thin layers or veneers from wooden logs. Such veneer lathes commonly use a pair of lathe chucks which support and rotate the log from which the veneer is being cut. Adjacent to the lathe chucks is the knife used to cut the veneers. The knife is usually supported on a knife carriage which also supports a nose bar which presses against the log immediately before the knife edge severs the veneer from the log. A great deal of force is necessary to turn the log against the knife and nose bar. This force must be carried by the log along its entire length which causes the log to deflect just like any beam under loaded conditions. Cutting the veneer from a deflected log produces a veneer which is not planar and also causes the log to become barrel shaped.
The prior art includes several inventions which were directed to maintaining the log in a coaxial position with the rotating lathe chucks by supporting the log with rollers at a point or points away from the knife edge. None of the prior art back-up rolls have proven to be entirely satisfactory. Some of the deficiencies or shortcomings of the prior art are discussed below.
Many of the prior art back-up rolls were very large and bulky machines which restricted access to the lathe chucks for loading logs. The bulkiness of the prior art back-up rolls was compounded by the fact that the back-up rolls were usually positioned over the lathe chucks, thereby preventing an overhead crane from being used to place logs in the lathe. Since an overhead crane could not be used, it was necessary to load the logs using forklifts or a charger arrangement. These loading techniques were more difficult than using overhead cranes and accordingly required greater amounts of time. Large bulky back-up rolls machines also restricted the operator's access to the log in order to clear slivers from the knife edge. Such slivers cause scarring of the veneer and are a routine problem during the operation of a veneer lathe.
Some prior art back-up roll machines were mounted upon the knife carriage. When a log would break or fly apart during the veneer cutting process a large force would be applied to the back-up rolls. This force would be carried through the knife carriage. In many instances the force applied to the back-up rolls would exceed the strength of the knife carriage arrangement causing brackets or other mounts to fail. This particular problem instigated the applicant's development of the current invention.
Many of the prior art back-up roll mechanisms used two rolls mounted on a pivotable plate so that the force applied by the rolls would approximately be balanced between the rolls by the automatic rotation of the plate. This arrangement was found to be unsatisfactory because the pivotable plate and rolls tend to oscillate or chatter because of waves or other surface roughness of the log. Occasionally the pivotable plate arrangement would cause the non-circularity of the logs to be aggravated by the fluctuating pressure applied by the back-up rolls as the out-of-round log would turn in the lathe.
Many of the prior art back-up rolls were hydraulically controlled. In most of these hydraulically controlled arrangements a given quantity of hydraulic fluid would be supplied to an operating cylinder. If there was any leakage in the hydraulic system the length of the hydraulic ram would become shorter and the support offered by the back-up rolls would be altered. This would change the veneer flatness and cause the log to become non-cylindrical. Hydraulically controlled back-up rolls also suffered from generally unsatisfactory operator control over the load being applied by the back-up rolls.
At least some prior art machines used followers which rode against the outside diameter of the log at a position near the lathe chucks. The desired back-up roll pressure or position of the back-up rolls was controlled from the information about the log size supplied by the follower. These arrangements were not entirely satisfactory because of irregularities in the surface contour of the log and because of the mechanisms used for translating the follower information into positioning of the back-up rolls.
Many prior art back-up roll systems did not provide appropriate or sufficient safety features so that operators could easily work in or around the lathe to clear chunks and slivers of wood. Even where provision was made for access, operational controls were not designed to facilitate the operator's quick and easy removal of chunks and return to the operating station.
Prior art back-up rolls generally did not provide an automatic feed system which allowed the operator to set the back-up rolls in an automatic position and to operate the lathe through a full cycle without touching the back-up roll controls. Nor did the prior art provide a system with total release of the back-up roll mechanism when a log flies apart in the lathe chucks.
Many prior art back-up roll systems did not provide for adequate adjustments for the roll positioning system to compensate for deflection of the lathe and back-up roll machinery. the structural frame of the lathe and back-up roll assembly were also often not sufficiently strong, causing substantial deflection in the machinery. Both of these problems caused the veneer to be non-planar. Vibration of the back-up roll system was also a problem in many prior art machines.
The applicant's invention seeks to solve the above problems of the prior art. The invention also contains other advantages and objectives which are set forth herein or which are implicit in the structure and function of the invention.